The treatment and pathophysiology of various renal disorders will be better understood if the GFR and RBF are measured. Problems with simple serum creatinine and 24-hour urine collections have led to the desire for a more precise method for their calculation. Different groups of patients currently are being treated here with Cyclosporine for Multiple Sclerosis, Membranous Lupus Nephritis, and Uveitis. The dosage of their Cyclosporine will be altered based on their GFR and ERPF and clinical condition. The studies are performed in the Nuclear Medicine Department following the injection and equilibration of the radiotracers. Timed blood and urine specimens are obtained and then counted to calculate the GFR and ERPF.